Corrosion under insulation (CUI) is corrosion that develops over time beneath thermal insulation used on pipes, tanks and other manufacturing and process equipment. Wherever piping, tanks or equipment are thermally insulated, there is potential for CUI. It is usually caused by condensation, rainwater, cleaning fluids, etc., that permeate into the insulation and attack the substrate to which it is applied. Impurities in the atmosphere and temperature gradients between tubulars and associated insulation also play a role in CUI development. Temperature gradients at the metal surface can lead to concentration of corrosive species, for example salts, which will accelerate the corrosion attack. Regardless of how securely insulation materials are applied to a substrate material, there will inevitably be areas where fluids can seep in, and where temperature gradients exist, thereby creating conditions that subsequently causes corrosion and damage to the substrate.
Detection of CUI in industrial plants has been identified as a significant problem, which can affect the integrity of tanks and pipes and lead to a shortening of the lifespan or even outright failure of expensive industrial infrastructure. Lengthy inspections and equipment failures often lead to manufacturing facility downtime, and consequently a loss of efficiency and increase in associated costs. CUI can be especially problematic wherever mastic is used as a finish, as well as around seals and metal ductwork, and wherever prior mechanical damage has occurred. As a consequence of CUI damage, a complete substrate replacement can ultimately become necessary.
One insidious aspect of CUI is that the corrosion is hidden from view by the thermal insulation. Typically, plants have miles of piping and thousands of square feet of insulation covered equipment. It is neither practical nor economical to remove the insulation at all locations for direct inspection. Traditionally, assessment of CUI has been handled manually using simple hand-held thermal imaging cameras to identify locations of wet thermal insulation. However, the accuracy of this equipment has been insufficient and costly due to “false calls,” which result in added expense due to the downtime associated with unnecessary removal and inspection of thermal insulation.
There is, therefore, a widespread but presently unmet need for an efficient and accurate detection system capable of identifying likely CUI corrosion sites in a variety of industrial manufacturing and processing environments.